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https://issues.apache.org/jira/browse/FLINK-15758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17024400#comment-17024400
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Till Rohrmann commented on FLINK-15758:
---------------------------------------
As
https://issues.apache.org/jira/browse/FLINK-14894?focusedCommentId=17024394&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17024394
says there is indeed a problem with higher memory pressure if the fix of
FLINK-14894 is applied. We reverted this fix momentarily and need to properly
fix this problem by monitoring the unsafe memory usage and trigger a clean if
required.
> Investigate potential out-of-memory problems due to managed unsafe memory
> allocation
> ------------------------------------------------------------------------------------
>
> Key: FLINK-15758
> URL: https://issues.apache.org/jira/browse/FLINK-15758
> Project: Flink
> Issue Type: Task
> Components: Runtime / Task
> Reporter: Andrey Zagrebin
> Priority: Major
> Fix For: 1.11.0
>
>
> After FLINK-13985, managed memory is allocated from UNSAFE, not as direct nio
> buffers as before 1.10.
> After FLINK-14894, the release of this memory happens only when all Java
> handles of the unsafe memory are about to be GC'ed. It is similar to how it
> was with direct nio buffers before 1.10 but the unsafe memory is not tracked
> by direct memory limit (-XX:MaxDirectMemorySize). The potential downside can
> be that over-allocating of unsafe memory will not hit the direct limit and
> will not cause GC immediately which will be the only way to release it. In
> this case, it can cause out-of-memory failures w/o triggering GC to release a
> lot of potentially already unused memory.
> If we should verify whether the delayed release is a problem then we can
> investigate further optimisations, like:
> * directly monitoring phantom reference queue of the cleaner (if JVM detects
> quickly that there are no more reference to the memory) and explicitly
> release memory ready for GC asap, e.g. after Task exit
> * monitor allocated memory amount and block allocation until GC releases
> occupied memory instead of failing with out-of-memory immediately
> cc [~sewen] [~trohrmann]
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